TAOISEACH Enda Kenny has expressed concern at the sizeable number of undocumented Irish citizens living in the US who must now "be brought in from the shadows".

Mr Kenny said he will fight for immigration reform measures "at the highest political level" which take into the account the 50,000 undocumented members of the Irish Disapora.

The US immigration system is not working properly, Mr Kenny said, and its flaws are having a major impact on Irish immigrants and their families.

The Taoiseach was speaking at an event in San Francisco which kicked off his three day trade mission to the West Coast.

He will today meet business leaders at a range of technical giants which have made significant investments in Ireland.

Addressing an audience at the United Irish Cultural Centre in San Francisco, Mr Kenny said the contribution by Irish to the development of the city cannot be understated.

"The Irish helped to build the roads and the railways; the dams and the water supply; they laid out the streets and built the buildings that line them. In so many ways San Francisco is built on the hard work of Irish immigrants and their children," he said.

Mr Kenny used his speech to express concern about the treatment of undocumented Irish citizens.

He said he raised the matter during his St Patrick's Day visit to the US but that he is cautious as to whether short term solutions can be found.

"Immigration reform offers an opportunity to solve a problem of enormous personal significance to an enormous number of people," Mr Kenny said.

"And it offers economic opportunity as well. American entrepreneurship, American innovation, American success is built on the contribution of immigrants," he added.

Mr Kenny told the audience that Ireland has made steady economic progress over the past twelve months, but that youth employment in particular remains too high.